Drill string rod with guidance shoulder

ABSTRACT

A drill string rod and a drill string assembly includes a drill rod and a drill bit. The rod includes a threaded male end and a female end. An axially extending shoulder is provided at the male end and has an axial length greater than an outside diameter of the shoulder to provide a shoulder driven rod exhibiting enhanced guidance to achieve straighter holes and better collaring.

FIELD OF INVENTION

The present invention relates to a drill string rod and a rod assembly to form part of a drill string having male and female ends separated by a main length section and in particular, although not exclusively, to a rod having an axially elongate shoulder configured to facilitate straight drilling and extraction of the bit end of the drill string.

BACKGROUND ART

Percussion drilling is used to create a long borehole via a plurality of elongate drill string rods coupled together end-to-end by interconnected male and female threaded ends. The well-established technique breaks rock by hammering impacts transferred from the rock drill bit, mounted at one end of the drill string, to the rock at the bottom of the borehole. Typically, the energy required to break the rock is generated by a hydraulically driven piston that contacts the end of the drill string (via a shank adaptor) to create a stress (or shock) wave that propagates through the drill string and ultimately to the base rock level. Conventional male and female threaded couplings are described in U.S. Pat. No. 4,332,502; U.S. Pat. No. 4,398,756; U.S. Pat. No. 1,926,925; U.S. Pat. No. 5,169,183; EP 1705415; GB 2321073; U.S. Pat. No. 4,076,436; U.S. Pat. No. 6,030,004; CA 2634557 and U.S. Pat. No. 4,687,368.

When the male and female threaded ends of neighbouring rods are coupled to create the drill string, the joint is typically subjected to bending forces during drilling. These bending moments fatigue the coupling and lead to breakage within the threaded portion of the joint. Additionally, there is a further risk that the drill bit, attached to the lowermost drill rod is subject to lateral deviation when drilling and becoming jammed in the borehole when the drill string is extracted. Drill bit deviation during initial boring (typically referred to as collaring) is also problematic with conventional arrangements. Attempts have been made to address such problems via the interconnection of a ‘coupler’ located between the drill bit and the lowermost rod. Such couplers are typically stiffer than the rods and are intended to be resistant to bending so that the drill bit travels faster and straighter during drilling. Example additional guidance couplers are described in WO 00/65192; U.S. Pat. No. 4,874,045; EP 0192622; CA 2550801 and US 2002/0050362. However, conventional and additional intermediate couplers are disadvantageous for a number of reasons. In particular, it is not uncommon for these additional pieces to be misplaced during use. Additionally, due to the inclusion of additional threaded connections, the efficiency of the shockwave transmission to the drill bit is reduced whilst stress in the entire drill string as a whole is increased. There is therefore a need for a drill rod and a drill rod assembly that addresses these problems.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a drill rod connectable to neighbouring drill rods and a drill bit that exhibits improved guidance via a shoulder driven percussion drilling system. In particular, it is an objective to provide a rod provided with a male and a female end in which the male end is configured to form an extension of the drill bit to achieve straighter and faster drilling and in particular improved collaring. It is a further specific objective to prevent or reduce the likelihood of the drill bit becoming jammed in the bore hole when the drill string is extracted.

The objectives are achieved by a drill rod having a main length section provided with male and female ends in which the male end is provided with an axially extended guidance collar or shoulder. The elongate shoulder is formed as a radially flared extension of the main length section to provide a stiffer threaded joint section suitable for coupling to female ends of adjacent rods and in particular a female threaded sleeve of a drill bit. The present dill rod is also particularly suitable for drilling relative small bore holes typically of a size approximately 54 mm and less.

The guidance shoulder of the male end of the present drill rod comprises an axial length that is greater than an outside diameter of the shoulder. That is, the guidance shoulder is flared radially outward relative to the main length section but also extends axially over a greater distance relative to conventional shoulder driven rods so as to form an elongate axial extension of the drill bit. In particular, the outside diameter of the shoulder is equal to or approximately equal to the outside diameter of an axially rearward mounting sleeve of the drill bit such that the shoulder of the rod and the rearward portion of the drill bit are interconnected to provide a single elongate cylindrical section having an outside diameter that is greater than the main length section of the rod. Such a configuration is effective to provide both the shoulder driven characteristic for percussion drilling and a system that is stiffer and comprises a potential deviation angle that is less than existing assemblies. Reference within this specification to the deviation angle encompass the angle by which the drill bit may rotate about its axis to the point where the cutting head end of the bit and/or an axially rearwardmost part of the shoulder contact the inward facing surface of the borehole.

According to a first aspect of the present invention there is provided a drill string rod to form part of a drill string, the rod comprising: a hollow elongate main length section extending axially between a male end and a female end; the male end comprising a spigot having a threaded section projecting axially from a shoulder that axially separates the spigot and the main length section, the shoulder having an outside diameter that is greater than an outside diameter of the main length section; characterised in that: an axial length of the shoulder over which the greater outside diameter extends is greater than the outside diameter of the shoulder.

The present shoulder configuration at the male end is applied to a drill rod in contrast to a third component of a drill string system, typically referred to as a ‘guide tube’ positioned at the bit end of the drill string axially intermediate the drill bit and the endmost drill rod. The present drill rod is advantageous to avoid the need for an additional guide tube that may be misplaced or damaged during use thereby preventing continued drilling. The present arrangement, being applied to a drill rod is advantageous to provide improved insertion and extraction at the drill bit at the borehole by increasing the collective stiffness of the drill string via the multiple male end sections present at each of the interconnected drill rods.

Preferably, an axial length of each elongate shoulder is less than an axial length of each main length section of each drill rod. The term ‘main length section’ may be defined as the axial distance between one axial end of the shoulder furthest from the spigot and one axial end of the sleeve (at the female end) furthest from the endmost annular face of the female end. That is, the main length section corresponds to the axial section of the drill rod between the radially enlarged shoulder and the radially enlarged female end.

Preferably, the shoulder comprises an axial length that is 5 to 40, 5 to 30, 5 to 20, 5 to 15, 7 to 13, 8 to 13 or 9 to 12% of an axial length of the main length section as defined between the axially inner ends of the shoulder and the radially enlarged female sleeve.

Preferably, the outside diameter of the shoulder is a maximum outside diameter of the rod.

Preferably the outside diameter of the shoulder is slightly less than the maximum outside diameter of a drill bit head to assist with guiding the driven rotation during advancement of the drill bit into the rock.

Preferably, the maximum outside diameter of the rod at the shoulder is uniform or approximately uniform over the axial length of the shoulder. Such a configuration is configured to be consistent with an axially rearward female cylindrical mounting sleeve provided at an axially rearward end of the drill bit such that the combined shoulder and drill bit sleeve form a single cylindrical section of uniform outside diameter.

Preferably, the female end comprises a sleeve portion having an internal threaded section to cooperate with the threaded section of the spigot of a further drill rod of the drill string, an outside diameter of the sleeve portion being greater than the outside diameter of the main length section. Preferably, the outside diameter of the shoulder is equal to or approximately equal to the outside diameter of the sleeve portion. However, according to further specific implementations, an outside diameter of the female sleeve may be less than the outside diameter of the shoulder. However, a configuration with equal outside diameters facilitates rod guidance to achieve straighter holes and extraction of the drill string from the bore.

Preferably, the spigot extends axially from an annular end surface of the shoulder, an axial length of the spigot configured such that the annular end surface of the shoulder is capable of abutting an annular end surface of the female end of a neighbouring rod of the drill string. Preferably the spigot is divided axially into a threaded section that represents an endmost part of the spigot and a non-threaded shank that is positioned axially intermediate the threaded end section and the annular end surface of the shoulder. Preferably an outside diameter of the shank is flared radially outward at the junction with the annular end surface of the shoulder to reduce stress concentrations and any lateral bending of the spigot relative to the shoulder. Optionally, an axial length of the spigot is less than or equal to the axial length of the shoulder.

Optionally, an outside diameter of the spigot is equal to or less than the outside diameter of the main length section along a full axial length of the spigot. Such a configuration provides an annular end surface at the shoulder configured to abut an annular end surface of a drill bit to achieve the desired shoulder contact coupled configuration.

Preferably, the rod comprises an internal bore extending axially through the main length section and the spigot, the internal bore being of uniform internal diameter along a full axial length of the main length section and the spigot. The uniform internal diameter provides the desired control of the pressure of a flushing fluid delivered internally through the rod to the drill bit.

Preferably, the threaded section of the spigot comprises at least one axially extending helical ridge and trough wherein the outside diameter along the threaded section at radial positions of the ridge and trough is uniform over a full axial length of the threaded section. Preferably, the threaded section comprises two helical turns extending axially over the spigot configured to mate with corresponding thread turns provided internally within a mounting sleeve of the drill bit and/or the internally threaded female end of neighbouring drill rods.

Optionally, the rod may comprise a transition section positioned axially at a junction of the main length section and the shoulder; wherein an outside diameter at the transition section changes according to at least one radius of curvature. Optionally, an outside diameter at the transition section decreases radially according to a first radius of curvature from the main length section to an intermediate section and the outside diameter increases radially according to a second radius of curvature from the intermediate section to the shoulder.

According to a second aspect of the present invention there is provided a drill rod assembly to form part of a drill string, the assembly comprising: a drill rod as claimed herein; a drill bit releasably attachable to the male end of the drill rod; the drill bit having an axially forward cutting head and an axially rearward mounting sleeve to attach to the male end of the drill rod; wherein an outside diameter of the mounting sleeve is equal to or approximately equal to the outside diameter of the shoulder.

Preferably, the outside diameter of the mounting sleeve is uniform or approximately uniform over an axial length of the mounting sleeve being defined between a rearwardmost end of the drill bit and an axially forwardmost end of the mounting sleeve at which region the outside diameter of the mounting sleeve increases to form a junction with the cutting head. The shoulder and mounting sleeve of the drill bit collectively define a single cylindrical section of constant outside diameter being slightly less than a maximum outside diameter of the drill bit head positioned axially forward of the mounting sleeve and the shoulder. Such a configuration is advantageous to achieve the desired pressure between the external surface of the rod and drill bit (at the region of the male end of the rod) and the internal facing surface of the bore to facilitate rearward flushing of material.

Optionally, the axial length of the shoulder is approximately equal to or less than an axial length of the mounting sleeve. Such a configuration reduces the deviation angle by which the drill bit may be deflected laterally including perpendicular to the longitudinal axis of the drill rod to achieve straighter holes and better collaring.

BRIEF DESCRIPTION OF DRAWINGS

A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

FIG. 1 is an external perspective view of a drill string rod coupled to a percussion drill bit according to a specific implementation of the present invention;

FIG. 2 is a cross sectional view through the drill rod and bit assembly of FIG. 1;

FIG. 3 is a perspective view of a male end of the drill rod of FIG. 2;

FIG. 4 is a further perspective view of the male end of the drill rod of FIG. 2;

FIG. 5 is a perspective view of the male of the drill rod of FIG. 2 coupled to the drill bit of FIGS. 1 and 2;

FIG. 6 is a cross section through the male end and drill bit of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

Referring to FIGS. 1 and 2, a percussion drill rod 100 comprises an axially extending main length section 101 that is terminated at a first end by a male end indicated generally by reference 103 and at a second opposite end by a female end indicated generally by reference 102. Rod 100 is capable of being coupled end-to-end with adjacent rods to form a drill string. Male end 103 comprises a shoulder 110 that projects radially outward relative to main length section 101 and is formed as a cylindrical section extending over an axial distance being a fraction of the length of main length section 101. Similarly, female end 102 comprises a cylindrical sleeve section 111 having a length approximately equal to the axial length of shoulder 110. According to the specific implementation, an outside diameter of shoulder 110 and female sleeve 111 are approximately equal. A respective transition section 107 extends axially between main length section 101 and the respective shoulder 110 and female sleeve 111. Each transition section 107 comprises an axial length being slightly less than the axial length of shoulder 110 and female sleeve 111. Additionally, an outside diameter of each transition section 107 is less than the outside diameter of main length section 101 as described in further detail referring to FIG. 4.

FIG. 1 illustrates drill rod 100 releasably coupled to a drill bit indicated generally by reference 112 of conventional configuration. Drill bit 112 comprises an axially forwardmost drill head 105 that mounts a plurality of wear resistant cutting buttons 106 projecting axially forward from head 105. A mounting sleeve 104 extends axially rearward from head 105 and comprises an internal threaded cavity to receive a male part of male end 103. In particular, and referring to FIG. 2, male end 103 comprises a spigot 204 that projects axially forward from shoulder 110 and in particular an annular abutment surface 108 that represents a forwardmost end of shoulder 110. Abutment surface 108 is positioned in contact with an annular endmost contact surface 109 of drill bit sleeve 104. According to the specific configuration, an axial length of spigot 204 is less than a corresponding axial length or depth of a cavity within bit sleeve 104 such that the present drill rod 100 is configured as a shoulder contact or shoulder driven rod. Accordingly, the shockwave generated by the surface piston is translated through mated surfaces 108, 109 from rod 101 into drill bit 112. In particular and referring to FIGS. 3 and 6, an annular endmost surface 303 of spigot 204 is separated axially from the innermost end 600 of the internal cavity within bit sleeve 104 to provide the shoulder contact configuration. As detailed in FIG. 6, releasable mating of rod 100 and bit 112 is achieved by cooperating screw threads 301, 302 projecting radially at spigot 204 and threads 601 projecting radially within the internal facing surface of the bit sleeve cavity.

Referring to FIG. 2, the female end 102 of rod 100 comprises an internal cavity 200 extending axially within sleeve 111 from an axially rearward end surface 202. End surface 202 of a first rod is configured to contact the shoulder abutment surface 108 of the male end 103 of a second rod when multiple drill rods 100 are coupled together end-to-end to form the drill string. Screw threads 201 are provided at the internal facing surface of sleeve cavity 200 and are configured to cooperate with the spigot threads 301, 302 of a neighbouring rod 100. An internal bore 203 extends axially through rod 100 and in particular axially from female cavity 200 to the annular end surface 303 of spigot 204. According to the specific implementation, bore 203 comprises an internal diameter that is substantially uniform over its entire axial length between the male 103 and female 102 ends.

Referring to FIG. 3 spigot 204 projects axially from the annular abutment surface 108 that extends substantially perpendicular to the cylindrical external surface at shoulder 110. Spigot 204 may be considered to be divided axially into threaded section 301, 302 and a non-threaded shank 300 that is positioned axially intermediate threaded section 301, 302 and shoulder 110. Shank 300 is flared radially outward relative to a longitudinal axis 305 of rod 100 at the junction 304 with annular abutment surface 108 such that the external surface of the shank 300 at the shoulder junction 304 increases according to a radius of curvature.

The threaded section of spigot 204 comprises a pair of helical ridges 302 that define axially intermediate troughs 301 extending between shank 300 and the annular spigot end surface 303. Referring to FIG. 4, an axial length L_(B) of spigot 204 including shank 300 and threaded section 301, 302 is less than an axial length L_(A) of shoulder 110. Shoulder length L_(A) is defined axially between annular abutment surface 108 (aligned perpendicular to axis 305) and an axially rearwardmost part of shoulder 110 at which the outside diameter of rod 100 decreases and is no longer uniform in the axially rearward direction from annular abutment surface 108. In particular, the rearward end of shoulder 110 is terminated by transition section 107. According to specific implementations, the axial length L_(B) may be in the range 60 to 100% or 75 to 85% of the axial length L_(A).

Section 107 may be considered to be divided into three axial regions including a first region 401 bordering main length section 101, a second region 402 bordering the rearward end of shoulder 110 and an intermediate region 400 positioned axially intermediate the first and second regions 401, 402. An outside diameter of rod 100 at the first transition region 401 decreases radially according to a first radius of curvature (relative to main length section 101). The outside diameter of rod 100 is substantially uniform over intermediate region 400 and then increases radially according to a second radius of curvature at second region 402. Accordingly, the outside diameter of rod 100 at transition section 107 is formed as an axially broad groove or slight depression positioned axially between main length section 101 and shoulder 110. The radially curved transition 304 minimises stress concentrations at the junction of spigot 204 and shoulder 110. Additionally, the radius of curvature at second transition region 402 minimises stress concentrations at the axially rearward end of the shoulder 110 and the junction with main length section 101.

Shoulder 110 comprises an outside or external diameter D_(A) being approximately equal to the outside diameter of female sleeve 111 at female end 102. Outside diameter D_(A) represents the largest outside diameter section of rod 100 along its entire axial length. A corresponding outside diameter of spigot 204 at the threaded section corresponding to a radial position at the peak of each helical ridge 302 is represented by D_(C) when D_(C) is less than D_(A). In particular, and according to specific implementations, D_(C) may be in the range 60 to 100% or 75 to 85% of D_(A). Additionally, an external diameter D_(B) of main length section 101 is less than the outside diameter D_(A) of shoulder 110 and according to specific implementations D_(B) is 70 to 100% or 85 to 99% of D_(A).

The enhanced drilling guidance and the capability of drilling straighter holes at increased rate is provided by the axial length of shoulder L_(A) being greater than the outside diameter of shoulder D_(A). When rod 100 is coupled to the drill bit 112 as illustrated in FIGS. 1 and 2, shoulder 110 effectively provides an axial extension of bit sleeve 104. In particular, and referring to FIG. 5, an outside diameter D_(E) of bit sleeve 104 is substantially equal to the outside diameter D_(A) of shoulder 110 such that the two cylindrical sections 104, 110 collectively define a single cylinder extending between bit head 105 and transition section 107 having a uniform diameter D_(A), D_(E) over its entire axial length being the combination of L_(A) and the axial length of the bit sleeve L_(C). It follows therefore that the shoulder axial length L_(A) is greater than the outside diameter D_(E) of bit sleeve 104.

Shoulder 110 effectively provides a linear extension of bit sleeve 104 that reduces the possible deviation angle of the bit 112 and male end 103 of rod 100 as it is both inserted and extracted from the hole. That is, any bending or lateral deviation, perpendicular to axis 305 within the bore at the region of bit 112 is reduced and is effectively restricted by the axial length L_(A) of shoulder 110 and in particular the axially rearward end of shoulder 110 contacting the internal surface of the bore. According to the specific implementation, an axial length L_(C) of bit sleeve 104 is defined between the annular contact surface 109 (at the axially rearward end of bit 112) and the axially forwardmost sleeve end 500 at which the outside diameter D_(E) increases to form the radially enlarged drill head 105. According to specific implementations, bit sleeve axial length L_(C) may be in the range 60 to 100% or 75 to 95% of the shoulder axial length L_(A). 

1. A drill string rod to form part of a drill string, the rod comprising: a hollow elongate main length section extending axially between a male end and a female end, the male end including a spigot having a threaded section projecting axially from a shoulder that axially separates the spigot and the main length section, the shoulder having an outside diameter that is greater than an outside diameter of the main length section, wherein an axial length of the shoulder over which the greater outside diameter of the shoulder extends is greater than the outside diameter of the shoulder.
 2. The rod as claimed in claim 1, wherein the outside diameter the shoulder is a maximum outside diameter of the rod.
 3. The rod as claimed in claim 2, wherein the maximum outside diameter of the rod at the shoulder is uniform or approximately uniform over the axial length of the shoulder.
 4. The rod as claimed in claim 1, wherein the female end includes a sleeve portion having an internal threaded section to cooperate with the threaded section of the spigot of a further drill rod of the drill string, an outside diameter of the sleeve portion being greater than the outside diameter of the main length section.
 5. The rod as claimed in claim 4, wherein the outside diameter of the shoulder is equal to or approximately equal to the outside diameter of the sleeve portion.
 6. The rod as claimed in claim 1, wherein the spigot extends axially from an annular end surface of the shoulder, an axial length of the spigot being configured such that the annular end surface of the shoulder is arranged to abut an annular end surface of the female end of a neighbouring rod of the drill string.
 7. The rod as claimed in claim 1, wherein an axial length of the spigot is less than or equal to the axial length of the shoulder.
 8. The rod as claimed in claim 1, wherein an outside diameter of the spigot is equal to or less than the outside diameter of the main length section along a full axial length of the spigot.
 9. The rod as claimed in claim 1, further comprising an internal bore extending axially through the main length section and the spigot, the internal bore being of uniform internal diameter along a full axial length of the main length section and the spigot.
 10. The rod as claimed in claim 1, wherein the threaded section includes at least one axially extending helical ridge and trough, wherein the outside diameter along the threaded section at radial positions of the ridge and trough is uniform over a full axial length of the threaded section.
 11. The rod as claimed in claim 1, further comprising a transition section positioned axially at a junction of the main length section and the shoulder, wherein an outside diameter at the transition section changes according to at least one radius of curvature.
 12. The rod as claimed in claim 11, wherein the outside diameter at the transition section decreases radially according to a first radius of curvature from the main length section to an intermediate section and the outside diameter increases radially according to a second radius of curvature from the intermediate section to the shoulder.
 13. A drill rod assembly to form part of a drill string, the assembly comprising: a drill rod including a hollow elongate main length section extending axially between a male end and a female end, the male end including a spigot having a threaded section projecting axially from a shoulder that axially separates the spigot and the main length section, the shoulder having an outside diameter that is greater than an outside diameter of the main length section, wherein an axial length of the shoulder over which the greater outside diameter of the shoulder extends is greater than the outside diameter of the shoulder; and a drill bit releasably attachable to the male end of the drill rod; the drill bit having an axially forward cutting head and an axially rearward mounting sleeve to attach to the male end of the drill rod, wherein an outside diameter of the mounting sleeve is equal to or approximately equal to the outside diameter of the shoulder.
 14. The assembly as claimed in claim 13, wherein the outside diameter of the mounting sleeve is uniform or approximately uniform over an axial length of the mounting sleeve being defined between a rearwardmost end of the drill bit and an axially forwardmost end of the mounting sleeve at which region the outside diameter of the mounting sleeve increases to form a junction with the cutting head.
 15. The assembly as claimed in claim 14 wherein the axial length of the shoulder is approximately equal to or less than an axial length of the mounting sleeve. 